Electrophotographic printer having image writing timed to prevent toner

Abstract

An electrophotographic printer includes a photosensitive drum, charging roller, image writing device, developing roller, and controller. The controller controls the operations of the image writing device and the developing roller so that a difference in potential between the surface of the photosensitive drum and the developing roller is below a firing potential. The controller causes the image writing device to fully emit light for a first predetermined time period immediately before completion of a printing operation, and for a second predetermined time period immediately after the printing operation starts, thereby bringing the surface of the drum to a potential nearly zero volts. The photosensitive drum stops rotating after the first predetermined time period and the photosensitive drum starts rotating immediately before the first predetermined time period. The photosensitive drum does not necessarily stop at exactly the same angular position after each printing operation. Likewise, the rising time and falling time of the bias voltage V.sub.B vary to some extent. In order to accommodate such variations, the controller compares an elapsed time after a preceding print operation has completed with a predetermined reference value. Then, the developing roller receives a bias voltage for the following print operation, the bias voltage being the same polarity as the surface oft he photosensitive drum charged by the charging device if the elapsed time is shorter than the predetermined value.